Ever since I've heard the name I've been confused. The space age is the shortest age I know of. It lasted a decade. Most ages are much longer. Most ages are generations.
"Age of Apocalypse" makes sense. Time travel was involved so that this new situation had been around for decades. (Two of them.) It's short, as ages go, but it lasts for a standard mathematical generation (twenty years) so it can be considered an age.
Ever since I've heard the name I've been confused, how can Ultron have an age in a single movie? The movie isn't going to follow the six generations of Avengers who formed the backbone of the resistance for all those years. The movie isn't going to end with everyone aged up by a decade.
I'm betting that it doesn't even have Ultron ruling earth for a single year (though I could be wrong on that point.)
The only explanation I've ever heard offered is that maybe there's great dispute over how old Ultron is. Has he reached the age of consent? Can he be tried as an adult? Did we miss his birthday?